1. Field of the Invention
The present invention relates to a temperature- and pH-sensitive oligomer hydrogel for drug delivery and a drug carrier using the same. More particularly, the present invention relates to a hydrogel composed of poly(amidoamine) (PAA) only and a drug carrier using the hydrogel.
2. Description of the Related Art
Drug carriers using polymer hydrogels have been developed. For example, U.S. Pat. No. 5,476,909 describes a biodegradable triblock (A-B-A) copolymer in the form of polyester wherein the hydrophobic blocks (A) are limited to polylactide (PLA), polyglycolide (PGA) and copolymers thereof, and the hydrophilic block (B) is limited to polyethylene glycol (PEG) and derivatives thereof.
The triblock copolymer consisting of the hydrophobic polymer and the hydrophilic polymer is sensitive to temperature and undergoes sol-gel transition in response to temperature changes. After the block copolymer in the form of an aqueous solution (i.e. a sol state) is injected into the body, it is changed to a gel state by the body temperature. This sol-gel transition enables the utilization of the block copolymer as a support of a sustained-release drug carrier that stably contains a drug and slowly releases and delivers the drug in the body. However, the sol-gel transition of the block copolymer sensitive to temperature only leads to a weak interaction with a drug, causing initial burst release of the drug after injection into the body. Further, the temperature of a syringe needle through which the block copolymer is injected into the body reaches thermal equilibrium with the body temperature. As a result, the block copolymer is gelled to clog the needle before it is completely injected into the body.